Fiber optic ribbons include optical waveguides such as optical fibers that transmit optical signals, for example, voice, video, and/or data information. Fiber optic cables using optical fiber ribbons can result in a relatively high optical fiber-density. Fiber optic ribbon configurations can be generally classified into two general categories. Namely, fiber optic ribbons with subunits and those without. A fiber optic ribbon with a subunit configuration, for example, includes at least one optical fiber surrounded by a primary matrix forming a first subunit, and a second subunit having a similar construction, which are contacted and/or encapsulated by a secondary matrix. On the other hand, fiber optic ribbons without subunits generally have a plurality of optical fibers surrounded by a single layer of matrix material.
Optical fiber ribbons should not be confused with micro-cables that, for example, have a strength member and a jacket. For instance, U.S. Pat. No. 5,673,352 discloses a micro-cable having a core structure and a jacket. The core structure requires that at least one optical fiber is positioned between longitudinally extending strength members, both of which are embedded in a buffer material. The jacket protects the core structure and the material is selected to have good adhesion to the buffer material and be abrasion resistant. Additionally, the strength members are required to have a larger diameter than the diameter of the optical fiber, thereby absorbing crushing forces that are applied to the cable.
On the other hand, optical fiber ribbons generally have a plurality of adjacent optical fibers arranged in a generally planar array forming a relatively high optical fiber density. Optical fiber ribbons without subunits can present problems for the craft. For example, when separating these optical fiber ribbons into optical fiber subsets, the craft must use expensive precision tools. Moreover, connectorization/splice procedures can require inventories of specialized splice and closure units/tools for the various subsets of optical fibers. Where the craft elects to separate the optical fiber ribbon into subsets by hand, or with a tool lacking adequate precision, stray optical fibers and/or damage to the optical fibers can result. Stray optical fibers can cause problems in optical ribbon connectorization, organization, stripping, and splicing. Additionally, damage to the optical fibers is undesirable and can render the optical fiber inoperable for its intended purpose.
However, there are fiber optic ribbon configurations that attempt to aid the separation of fiber optic ribbons without using subunits. For example, U.S. Pat. No. 5,982,968 requires an optical fiber ribbon of uniform thickness having V-shaped stress concentrations in the matrix material that extend along the longitudinal axis of the fiber optic ribbon. V-shaped stress concentrations can be located across from each other on the planar surfaces of the fiber optic ribbon, thereby aiding the separation of the fiber optic ribbon into subsets. However, the '968 patent requires a wider fiber optic ribbon because additional matrix material is required adjacent to the optical fibers near the V-shaped stress concentrations to avoid stray optical fibers after separation. A wider ribbon requires more matrix material and decreases the optical fiber density. Another embodiment of the patent requires applying a thin layer of a first matrix material around optical fibers to improve geometry control such as planarity of the optical fibers. Then V-shaped stress concentrations are formed in a second matrix applied over the first matrix material, thereby allowing separation of the subsets at the stress concentrations.
Another example of a separable fiber optic ribbon is described in U.S. Pat. No. 5,970,196. More specifically, the '196 patent requires a pair of removable sections positioned in V-shaped notches located across from each other on opposite sides of the planar surfaces of an optical fiber ribbon. The removable sections are positioned between adjacent interior optical fibers of the optical fiber ribbon to facilitate the separation of the optical fiber ribbon into subsets at the V-shaped notches. The removable sections can either be flush with the planar surfaces of the optical fiber ribbon, or they may protrude therefrom. These known fiber optic ribbons have several disadvantages. For example, they can be more expensive and difficult to manufacture. Additionally, from an operability standpoint, the V-shaped stress concentrations and/or V-shaped notches can undesirably affect the robustness of the optical fiber ribbon and/or induce microbending in the optical fibers.
Fiber optic ribbons that employ subunits to aid separation generally do not encounter these problems; however, they can have other problems. A conventional optical fiber ribbon 1 employing subunits encapsulated in a secondary matrix is shown in FIG. 1. Optical fiber ribbons having subunits can have several advantages, for example, improved separation, and avoidance of stray fiber occurrences. In particular, optical fiber ribbon 1 includes a pair of conventional subunits 2 having optical fibers 3 encapsulated in a primary matrix 5, which are then encapsulated in a secondary matrix 4. The thickness T1 of primary matrix 5 is continuous and uniform. Likewise, the thickness t1 of the secondary matrix 4 covering the planar portions of subunits 2 is continuous and uniform. For example, subunit 2 can include six 250 μm optical fibers 3 disposed in primary matrix 5 having an overall uniform thickness T1 of 310 μm and secondary matrix 4 has a thickness t1 of 10 μm for an overall fiber optic ribbon thickness T2 of 330 μm.
However, conventional optical fiber ribbon 1 has disadvantages. For example, one concern is the potential formation of wings W (FIG. 1) during hand separation of subunits 2. Wings W can be cause by, for example, a lack of sufficient adhesion between common matrix 4 and subunit matrix 5 and/or random fracturing of the secondary matrix during separation. The existence of wings W can negatively affect, for example, optical ribbon organization, connectorization, stripping, and/or splicing operations by the craft. Additionally, wings W can cause problems with ribbon identification markings, or compatibility of the subunit with ribbon handling tools, for example, thermal strippers, splice chucks, and fusion splicers.